1. Field of Invention
This invention relates to a means for enhancing the safety of electrical devices which expose persons to the hazards of electromagnetic fields.
2. Description of Prior Art
Within the past decade, researchers have reported higher risks of disease by users of electric blankets, waterbed heaters, ceiling heating elements and other electrical devices.
After doing some basic research with the effects of electromagnetic fields and currents, this inventer concluded that the reason electromagnetic fields can be hazardous at the field strength commonly encountered is due to the fact that the field intensity changes with respect to time. This led to the conception of a device that would limit the changing nature of the power provided for use. These conclusions were confirmed by testing a number of proto-types that incorporated these ideas.
This testing has identified four sources of hazardous fields.
They are:
(a) the basic operating frequency of the power generator, 60 hertz being the most common.
(b) a broad spectrum of frequencies picked up by power lines from a number of different sources.
(c) switching and power control.
(d) ambient sources of electromagnetic fields and radiation not connected with the device being used.
The testing done here did not reveal any negative effects from 100 milligauss or less constant magnetic fields. These field intensity levels are greater than most common domestic electrical devices generate. However, when exposed to time varying field intensities, negative reactions were observed most of the time. Some positive reactions were observed for some frequencies for short periods of time.
When a person is exposed to 50 hertz, 60 hertz or other random frequencies, negative reactions were observed most of the time. If some very small negative effects from the converted constant magnetic field are present, they are undetectable by any testing method available. Whatever the outcome of future research on this subject, the evidence collected as of this date clearly shows that the major portion of the hazards of electromagnetic fields is due to the intensity changes with respect to time.
If it becomes necessary to change the current level for control purposes or for other reasons, then this change should be made as gradually and slowly as possible or practical. The inventer has given this process the nicknames, "power softening" or "field softening". Also, a device that performs this function is referred to as a "power softener" or "field softener".
One theory that can explain this, is the law or theory of magnetic induction. The theory of magnetic induction states that any conductor in a magnetic field that is changing in strength with respect to time will have a voltage induced upon it, and that voltage is proportional to the rate of change of magnetic field intensity. If living systems are in a changing magnetic field, then electric currents would be generated within these systems, thus inducing stresses upon these living systems. By reducing the switching rate, higher induced voltages in biological systems can be avoided.
A prior patent which addresses this problem is an expensive and elaborate shielding device for heating pads and electric blankets, U.S. Pat. No. 4,931,625 to Marlinski (1990).
Another prior patent that is more closely related to this patent application is U.S. Pat. No. 5,036,177 to Pagliarini (1991). This patent does protect the user from the primary alternating current frequency but offers little protection to other electromagnetic hazards such as switching and nearby ambient fields.
Also the Pagliarini patent rectified and filtered prior to the control circuits, and as a result, this would cause the controls in some electric blankets to malfunction. This is because the current ratings of some bi-metal control contacts are marginal for the ac power applied and are not able to operate with the same power levels with dc. However, the scheme proposed here, filtration after the control process, eliminates this problem as well as providing better protection to the user.